The invention pertains to a digital device for detecting the hold by an apparatus of a telephone line into which is plugged a so-called duplex band superposition transmission modem. It also relates to a band superposition transmission modem.
A band superposition transmission modem makes it possible, by superposition, to send and receive data, generally digital, simultaneously in the same frequency band, travelling through telephone lines.
For the sending or receiving of data, it is common to use telephone lines which are used moreover for other uses such as customary telephone communications. Such are thus, in particular, television decoders.
These decoders can be linked automatically, by way of the modem, to a program provider without the user of the telephone line being informed of the moment of the communication.
In general, so as not to disturb the common use of the telephone line, the modem must be such that it gives priority to telephone communications, that is to say that, if the modem occupies the line, it must disconnect itself if the user seeks to use the line.
Now, present-day modems employing band superposition transmission do not have any device for detecting line hold so as to be able to assign such priority.
The aim of the present invention is in particular to remedy this major drawback.
To this end, the subject of the invention is a digital device for detecting the hold by an apparatus of a telephone line into which is plugged a modem employing band superposition transmission, the modem sending a send signal on the telephone line and receiving from this line a digitized reception signal, characterized in that the said device comprises:
a means for providing a parameter of the transfer function of the send signal on the reception signal, the said parameter being characteristic of the presence of at least the said apparatus on the line,
control means for controlling the interruption of the exchanges of signals of the modem on the line, the said control being dependent on the said parameter of the transfer function.
Thus, the user of the telephone line desiring to use the latter is not disturbed by the modem. Moreover, because it is totally digital, the device of the invention makes it possible to carry out an accurate estimation of the transfer function insofar as the signals are not affected by temperature drifting.
Advantageously, the said means for providing the parameter of the said transfer function comprises a processor implementing a step of estimating the static gain of the transfer function K and a step of determining the sign of the estimated static gain. Thus, the said steps of estimation and of determination can be performed by a program installed in a processor generally located in the modem or in any associated decoder.
According to one embodiment, the step of estimating the static gain of the transfer function comprises a step of calculating the coefficients of the transfer function implementing an identification algorithm of the Kalman or RLS type or the method of least squares.
According to one embodiment, the device according to the invention includes a means for disconnecting the modem from the line when the said device sends an indication signal that the line is requested by the apparatus plugged in in parallel.
The subject of the invention is also a band superposition transmission modem, characterized in that it includes a detection device according to the invention.
The subject of the invention is also a server of an Internet network access provider, characterized in that it comprises a device according to the invention or a modem according to the invention.
The subject of the invention is also a method of detecting the hold by an apparatus of a telephone line into which is plugged a modem employing band superposition transmission, the modem sending a send signal on the telephone line and receiving from this line a digitized reception signal, characterized in that the said method includes the following steps:
a step for providing a parameter of the transfer function of the send signal on the reception signal, the said parameter being characteristic of the presence of at least the said apparatus on the line,
a control step for controlling the interruption of the exchanges of signals of the modem on the line, the said control being dependent on the said parameter of the transfer function.
According to one embodiment, the step for providing the parameter of the transfer function of the send signal on the reception signal comprises a step of estimating the static gain of the transfer function and a step of determining the sign of the estimated static gain.
According to one embodiment, the step of estimating the static gain of the transfer function comprises a step of calculating the coefficients of the transfer function implementing an identification algorithm of the Kalman or RLS type or the method of least squares.
According to one embodiment, the method of detection is performed continuously during the phase of modem data exchange with the telephone line.